cxa.4

<B>Digital的Unix操作系统VAX 4.2源码</B>

.TH cxa 4
.SH Name
cxa \- CXA16 communications interface
.SH Syntax
.B "device dhu0 at uba0 csr 0160440 flags 0xffff vector dhurint dhuxint"
.SH Description
.NXR "CXA16 communications interface"
A CXA16 provides 16 data-leads-only communication lines with no modem control.
.NXR "RS423A standard"
The CXA16 conforms to RS423A.
The device behaves and looks just
like a DHV11
(with the exception of modem control and number of lines)
and is specified in the configuration line the same
as a DHV11 device.
Each line attached to the CXA16 communications multiplexer
behaves as described in
.MS tty 4
and can be set to run at any of 16 speeds; see
.MS tty 4
for the encoding.
.PP
A flags field of 0xffff must be used to specify 
that all lines are to operate
as hardwired.  This is done to prevent the line from being treated as a
modem control line.
.PP
The dhu driver normally interrupts on each input character.
.NT
The 
.PN cxa ,
.PN cxb ,
.PN cxy ,
.PN dhv , 
and
.PN dhq
devices operate under the control of the 
.PN dhu
driver.
.SH Diagnostics
.B "dhu%d: receive fifo overflow"
.br
The character input fifo overflowed
before it could be serviced.  This can happen if a hard error occurs
when the CPU is running with elevated priority, as the system 
then prints a message on the console with interrupts disabled.
This can cause a few input characters to be lost to users.
It is not serious.
.PP
.B "dhu%d:%d DMA ERROR
.br
A DMA transfer error has occurred.
The
.PN cxa
unit number and line number are printed.
This means that the channel indicated has failed to transfer DMA data
within 10.7 microseconds of the bus request being acknowledged or that
there is a memory parity error.
This may cause a few output characters to be lost.
.PP
.B "dhu%d: DIAG. FAILURE"
.br
This indicates that the
.PN cxa
internal diagnostics have detected an error.
.PP
.B "dhu%d: DHU HARDWARE ERROR.  TX.DMA.START failed"
.br
The 
.PN cxa 
failed to clear the start bit.  Normally, this 
is cleared to signal 
that a DMA transfer has completed.
.SH Files
.PN /dev/tty??
.SH See Also
tty(4), MAKEDEV(8)